Hi Heather,
yes you can use haiku as a simple web server.
https://www.haiku-os.org/docs/userguide/en/applications/poorman.html
This said it means a really simple server, no php no mysql and so on.
There is a apacheserver, php and mysql port at haikuware (for the alpha 4 version)
http://www.haikuware.com/directory/view-details/internet-network/servers/apache/139-php/535-mysql/557-rc-bundle
Also so its possible to use Haiku as a web server,it dont support stuff wich you want to have for a productive enivorment.
e.g. a raid system or so.